1) Field of the Invention
The present invention relates to a method for producing crystals of purine nucleotide derivative disodium, which are important as flavorings and pharmaceutical products. More particularly, the present invention relates to a method for removing an alcohol such as methanol, from purine nucleotide derivative disodium crystals that efficiently removes the alcohol, from crystals containing methanol, for example, those crystals obtained by crystallization from methanol (hereinafter, also “methanol crystallization”). Furthermore, the present invention relates to a method for producing purine nucleotide derivative disodium crystals that involves the use of the method for removing methanol (hereinafter, also “methanol removing method”).
2) Description of the Related Art
Crystals of purine nucleotide derivative disodium such as crystals of 5′-guanylic acid disodium (hereinafter, “5′-GMP2Na”) are important for producing flavorings and pharmaceutical products. The purine nucleotide derivative disodium crystals are obtained by crystallization in the copresence of methanol. However, methanol in the crystals in unacceptable amounts unless any other treatment is performed. When the purine nucleotide derivative disodium crystals are used for application to food or pharmaceutical products, it is necessary to reduce the content of methanol to a predetermined upper limit.
Purine nucleotide derivative disodium crystals such as 5′-GMP2Na crystals contain about 23% to about 24% of water as crystal water. Since methanol is present mostly in the crystal water, it is difficult to remove it from the crystals unlike the case where methanol or ethanol is attached to the surface of crystals. For example, when crystals are obtained in a system in which methanol coexists and allowed to stand at ambient temperature (e.g., about 20±15° C.), considerable amounts of methanol remain in the crystals; for example, about 100 parts per million of methanol remains in the crystals even after 24 hours. Similar problems are encountered when crystals of purine derivative nucleotide disodium crystals are formed in ethanol or a mixture of methanol and ethanol.